Under the rapid economic development in the urban area of cities in Southeast Asia, consideration to environmental protection has simultaneously advanced.

At the landfill site, the condition of landfill has been dramatically improved with countermeasures such as installation of bottom layer to avoid seepage of the wastewater from the waste layer, and soil covering for the prevention of waste scatters, insect and odor occurrence.

The characteristics of landfilled waste are also different after introducing the waste separation at source and intermediate treatment.

Though technology for municipal solid waste management has advanced, treatment of leachate from landfill has remained unchanged. Methods such as applying leachate pond and discharge to the soils are applied in many landfills and not much improvement has been progressed until now.

In the urban area of Southeast Asian cities, huge amount of leachate is generated during rainy season and the varieties of waste have diversified. Therefore, it is important to propose the landfill leachate treatment as part of the comprehensive waste management system according to the environmental condition of Southeast Asian region. Our research center at NIES preliminary aims to provide the solution. Our research contributes to the proposal of leachate treatment technology and system considering the development level of solid waste management in each country, and information and data acquisition to provide smooth technology transfer.

Wastewater treatment technology based on ecological engineering

生態工学的な排水処理技術

Though economy has been developing in Southeast Asian region rapidly, it is almost impossible to use vast amount of cost and energy for the leachate treatment at landfill sites in the region. Therefore, we have been trying to develop the waste treatment technology using constructed wetlands which requires little electricity.

Wastewater treatment by constructed wetlands is simply inputting wastewater for treatment and does not require complicated system.

In addition, not only microorganism and micro fauna exists in the wetlands, but also animals such as frog that prey on microorganism and micro fauna. Organics and nutrient salts circulate ecologically in the system are also created by wetlands. Based on the characteristics of Southeast Asia with high humidity and precipitation, our research center at NIES conducts fundamental research on water balance in the wetlands considering rain inflow and volume of water evaporation at our outdoor research investigation facility. Results of the research are under consideration to be applied in Southeast Asian region.

Testing of landfill leachate treatment in Thailand

We are conducting small scale test using landfill leachate under the tropical climate condition in Thailand. Cattail was selected for wetland because it has grown in the landfill site and as you can see, it has grown well in the constructed wetlands. We assume the cattail acclimated to the salty leachate treatment.

Photo: Ongoing testing of constructed wetlands model in Thailand

Objective of constructed wetlands is predominately water quality control; however, we are also focusing attention on the volume of water. When leachate inflows into the constructed wetlands, the volume of leachate decrease by evaporation and plant transpiration. It leads to the decrease in volume of treated water compare to the original leachate inflow. In this testing, we identify the 40% decrease of water volume in total and especially the rate accelerates in the daytime. If volume of water can be controlled effectively, post treatment would be much easier and eventually makes the landfill water management more effective.

In our ongoing research, we will analyze the factors for treatment how does factors such as water quality in the original leachate, pattern of leachate inflow, rainfall condition and permeability of filter element affects growth of plant, volume of evaporation and water treatment performance. Ultimately, we aim to acquire a set of parameters for practical use.

Greenhouse gas

When wastewater is treated in the usual manner, potent greenhouse gases methane and nitrous oxide are produced due to the bacterial decomposition of pollutants. At constructed wetlands, it also emits the greenhouse gas. However, the gas production mechanism is rather complicated due to the ecological effect at the constructed wetlands.

At wastewater treatment plant, generally activated sludge process is used. Activated sludge consists of bacteria, protozoa and metazoa. On contrary at constructed wetlands site, plants and small animals are harbored in addition to microorganism and micro fauna. This ecosystem may affect the emission of greenhouse gas, and various environmental factors such as climate, insolation condition have effects on the ecosystem.

Intergovernmental Panel on Climate Change (IPCC) sets the calculation method of amount of greenhouse gas emissions based on the scientific knowledge for the usual wastewater treatment. However, since calculation method of greenhouse gas emission for constructed wetlands did not exist, guideline for constructed wetlands has supplemented to the IPCC guideline where the author took part as one of the Coordinating Lead Authors to this supplementary guideline.

Further activities

In this study, we also experiment controlling the environmental condition inside the landfill by re-inputting landfill leachate into the landfill again for microorganism decomposition in the waste layer and chemical stabilization. Circulating the leachate avoids excessive consumption of scarce water resources. Taking the volume volatility of water in the rainy season and dry season in the tropical climate into consideration, it is necessary to develop the appropriate leachate treatment technology that allows removing the pollutant substances. We are currently combining different technologies from constructed wetlands to the advanced membrane treatment technology for the landfill leachate treatment and aims the research is turned into practical use.

In recent years, planting duckweed has proven to be attractive for water quality control. Duckweed is effective in promoting removal of aromatic compound such as phenol, aniline and nonyl-phenol, and some aromatic compound degrading bacteria have been separated from the roots of duckweed. In the future, we are planning to expand the scope of research with harmonious coexistence of duckweed and effective microorganism for the landfill leachate treatment and test to remove the pollutant substances and heavy metals from the leachate.

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